Lubricants containing mixed metal salts of fatty acid and aromatic polybasic acid



United States Patent ice Patented 3 33, 3

clude: o, In, or p-phthalic acid and the various other acids whose structures follow:

LUBRICANTS CONTAII IING MIXED METAL 5 coon ooon SALTS 0F FATTY ACID AND AROMATIC l POLYBASIC ACID C O OH Arnold J. Morway, Clark, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware H000 G O OH No Drawing. Filed Apr. 1, 1964, Ser. No. 356,661

6 Claims. (Cl. 252-41) 10 (1)0011 (trimellitie) (trimesic) C 00H 0 O OH Th1s invention relates to lubricants comprising lubr1cating oil containing alkali metal mixed salts of fatty acids OOOH and certain aromatic polybasic acids as additives or as grease thickeners. O OH HO O Q O OH In its preferred form, the inventlon relates to lubricating grease suitable for lubrication of anti-friction bearings (hemilnellitic) (mellophanic) comprising lubricating oil thickened with a mixture of alkali metal salt of fatty acid, which is preferably a mix- COOH ture of low molecular weight fatty acid and a higher molecular weight fatty acid, and acomatic polycarboxylic H0OC OOOH 'OOOH acid, in certain molar equivalent proportions. The v greases of the invention differ from previously known, HOOC COVOH 0003, related alkali metal high temperature bearing greases I 0 OH wherein the thickener is a mixed salt of low molecular Y I (pyromelhtic) (prelmit c) weight fatty acid, e.g. acetic acid, and higher molecular weight fatty acid, e.g..C to C fatty acid. Thus, in contrast I Said Previously known greases, h greases of 30 Where they exist, the corresponding partial or full acid the invention do not become excessively fluid at elevated ahhydrides may also he used; phthahc anhydride'oh temperatures, or become excessively rubbery or fibrous at pyromelhtih acid ahhydride Which has the Structure: elevated temperatures, due to phase changes in the soapthickening structure.

The mixed-salt systems of the invention are best made 0 0 to contain alkali metal salt of 0.5 to 6.0, preferably 2 to 4, L g molar hydrogen equivalents of low molecular weight C to C fatty acid per molar hydrogen equivalent of aro- O O matic polycarboxylic acid, These systems will also contain salt of 0.5 to 3.0, preferably 1 to 2 molar hydrogen 40 0 equivalents of higher molecular Weight fatty acid, e.g. II it C to C fatty acid, per molar hydrogen equivalent of 0 0 said aromatic acid. Greases can be thus prepared having a total content of these carboxylic acid salts of 5.0 to

40.0 weight percent, preferably 10 to 35 weight percent,

alkali metal, preferably lithium or sodium or mixtures The metal component of the mixed thickeners is an based on the weight of the greast. These greases in turn th fl can be diluted with additional oil to form fluid or semilubricating oil used in the compositions of tha flu id compositicms containing about to 53% of the invention may be either a mineral lubricating oil or a mlxed Saltsynthetic lubricating oil. Synthetic lubricating oils which Suitable low molecular weight fatty acids include C may bg used inchlde (esters f dibasic acids (e g 2 to C fatty a id u as acetic, PI P butyric, ethylhexyl sebacate), ester of glycols (e.g. C oxo acid Acetic acid its anhydrid? is preferred' diester of tetraethylene glycol), complex esters (e.g. the The high molecular Welght fatty acid includes 10 to complex ester formed by reacting one mole of sebacic 30 {latlll'ally-occurring of Synthetic sulistituted or 55 acid with two moles of tetraethylene glycol and two moles substltuied, Saturated or u'nsatufatedi mlxed unmlxed of Z-ethyl-hexanoic acid), halocarbon oils, alkyl silicates,

aCldS. Preferred aCldS W11]. have to carbon ulfite esters mercaptals formals type ynatoms P molecule- Examples 0f Such acids include thetic oils, etc, or mixtures of any of the above in any myristic, Palmitic, Stearic, y v Steafic, Brachidic, proportions. If the salts are formed in situ in the oil, Oleic, TiIlCinOleic, hydrogenated fish tallOW acids, etc. then this in situ reaction is best carried out in a mineral The aromatic polycarboxylic acids used in this invenoil, since many synthetic oils will tend to decompose or tion are those having 2 to 4 carboxylic acid groups per hydrolyze during the salt formation. However, the salts benzene ring, which carboxylic acid groups can be in the once formed, can be used in lubricants containing the ortho, meta or para position. These aromatic acids insynthetic oils noted above. a

It has been further found that coneutralizing phosphoric acid along with the other acids can further improve the lubricant. Specifically, not only does a harder grease result but the metal phosphate imparts anti-oxidation properties and increases the lubrication life of the grease. Usually, about 0.1 to 6.0, preferably 1.0 to 5.0 wt. percent, of ortho phosphoric acid will be used.

The lubricants of the invention can be formed in a number of different ways. The most convenient is to neutralize the acids, in at least a portion of the oil, with an aqueous solution, e.g. to 90 wt. percent water, of the alkali metal base. Usually, the grease will be milled to a smooth consistency before dehydrating since the wet grease is easily homogenized or milled. Usually, the resulting composition will then be heated and dehydrated at about 300 to 550 F., preferably 400 to 500 F., then cooled, and any additives used are then added. Usually, the cooled grease will be further homogenized.

Various other additives may also be added to the lubricating composition (6g. 0.1 to 10.0 wt. percent) of oxidation inhibitors such as phenyl-alpha-naphthylamine; corrosion inhibitors such as sodium nitrite and sorbitan monooleate; dyes; extreme pressure agents; tackiness agents; other grease thickeners, and the like.

The invention will be further understood by reference to the following examples wherein all parts are by weight.

EXAMPLE I 72.2 parts of mineral lubricating oil of about 60 SUS viscosity at 210 F., parts of Hydrofol Acid 51 and 3 parts of phthalic anhydride were added to a fire-heated kettle and stirred while heating to 130 F. Then 5.8 parts of lithium hydroxide monohydrate, in the form of an aqueous solution consisting of wt. percent of said monohydrate and 80 wt. percent water, was added to the mixture. This was followed immediately by the addition of 3 parts of glacial acetic acid. The neutralized composition was then mixed for 30 minutes, after which the wet grease, which had a temperature of about 200 F. due to the heat of reaction, was cycled through a Charlotte mill having an 0.008" opening and then passed back to the kettle until all lumps and small specks had been eliminated and a smooth homogeneous grease was obtained. Without milling at this stage, the small specks of undispersed salts and soaps, if heated and dehydrated, connot be effectively eliminated by milling at a latter stage. The smooth, wet milled grease was then heated to a temperature of about 440 F., which was maintained for about a half hour in order to dehydrate and fully disperse the salts in the oil. Heating was then discontinued and the grease was allowed to cool to 250 P. where one part of phenyl-alpha-naphthylamine was added. The grease was then cooled to 120 F. and passed again through the Charlotte mill to :form a finished grease.

The Hydrofol Acid 51 used above is hydrogenated fish oil having a degree of unsaturation and average chain length similar to stearic acid.

EXAMPLE II 78.36 parts of mineral lubricating oil (60 SUS viscosity at 210 F.), 10.85 parts of Hydrofol Acid 51 and 2.01 parts of phthalic anhydride were added to a fireheated kettle and stirred while heating to 130 P. Then, 3.9 parts of lithium hydroxide monohydrate in the form ofan aqueous solution (20 wt. percent lithium hydroxide monohydrate) was added, followed immediately by the addition of 201 parts of glacial acetic acid. After mixing for 30 minutes, the wet grease which was now at a temperature of about 200 F. was passed through a Charlotte mill having an 0.003 clearance and recycled back to the kettle until homogeneous grease was obtained. The smooth, wet, milled grease was then heated to a temperature of about 440 R, which was maintained for about 0.5 hour, in order to completely dehydrate and complex the salt composition. Heating was then discontinued and the grease was cooled to 250 E, where 0.67 part of phenyl-alpha-naphthylamine was added as an oxidation inhibitor. The grease was then further cooled to 120 F., after which 3 parts of a 50/50 by weight mixture of sodium nitrite dispersed in mineral lubricating oil having a viscosity of 300 SUS at F. was added. The sodium nitrite used here had an average particle size of about 30 microns. After the sodium nitrite dispersion was added, the grease was then homogenized by passage through a Charlotte mill.

EXAMPLE III A grease was prepared in the same manner as that of Example 11 except that pyromellitic dianhydride was used in place of the p-hthalic anhydride and the propor tions of the various ingredients differed from those of Example II.

Composition A A grease was prepared representing the prior art and which was similar to the greases of the examples except that no aromatic acid was used. This grease was prepared as follows:

76.8 parts of mineral lubricating oil and 15 parts of Hydrofol Acid 51 were added to a fire heated kettle and stirred While heating to 130 F. Then 4.3 parts of lithium hydroxide monohydrate in the form of an aqueous solution (20 wt. percent lithium hydroxide monohydrate) was added to the mixture, followed immediately by the addition of 3 parts of glacial acetic acid. The composition was then mixed for 30 minutes, after which the wet grease, which had a temperature of about 140 F., was cycled through a Charlotte mill having an 0.003 opening and then passed back to the kettle until all lumps and small specks had been eliminated. The smooth, wet milled grease was then heated to a temperature of about 440 R, which temperature was maintained for about one-half hour in order to dehydrate and complex the mixture. Heating was then discontinued and the grease allowed to cool to 250 P. where one part of phenylalpha-naphthylamine was added. The grease was then cooled to F. and homogenized in a Gaulin homogenizer to form a finished grease.

Composition B This grease was a simple lithium hydroxy stearate grease and represents a grease without salts of either the low molecular weight fatty acid or the aromatic acid. This grease was prepared as follows:

10 parts of 12-hydroxy stearic acid was charged to a fire-heated kettle along with 87.5 parts of mineral lubricating oil and mixed While heating to F. Then 1.5 parts of lithium hydroxide monohydrate (in the form of an aqueous solution containing 20 wt. percent lithium hydroxide monohydrate) was added. Heating was then initiated and the composition was heated to a temperature of 390 R, which was maintained for about onehalf hour and the entire composition was totally dehydrated. The composition was then cooled to 250 P. where one part of phenyl-alpha-naphthylamine was added as an oxidation inhibitor. The composition was then cooled to 120 F. and then homogenized in a Morehouse mill, after which it was packaged.

The formulations of the above examples and comparison compositions, along with their physical properties are summarized in the following table:

What is claimed is:

1. A lubricating grease consisting essentially of a major TABLE Examples Comparison Compositions Composition (Wt. Percent) I II III A B Hydrofol Acid 51 15.0 10. 05 10. 15. 0 Glacial Acetic Acid 3. 0 2. 01 2. 0 3. 0 Phthalic Anhydride 3. 0 2.01 Pyroruellitic Dianhydride 2. 0 12-Hydroxystearie Ar 10.0 Liorrmo 5.8 a. 90 4. 2 4. 3 1. 5 Phenyl-a-uaphthylamine 1. 0 0. 67 1. 0 1. 0 1. 0 50% NaNO dispersed in 50 wt. percent mineral lubricating oil 3. 3. 0 Mineral lubricating oil, so SUS at 210 F. 72. 2 78. 36 77.8 76.8 87.5 Mole eq. ratio-higher fatty acid/al'omati hydrirle 1. 5 1. 5 2. 2 Mole eq. ratio-acetic acid/aromatic anhydride 1.4 1.4 2. 1 Properties:

Appearance Dropping Point, F 450 405 410 ASTM Penetration, 77 F mm Unworked. 215 270 280 Worked 60 strokes. 222 280 285 Worked 10,000 strokes..." 190 280 300 Water Solubility, Boiling Water.

Norma Hoffman Oxidation:

100 hrs. 2 p.s.i. drop 500 hrs. 5 p.s.i. drop Lubrication Life, *Hours, 10 000 r.p.m.:

1 Excellent. 2 Faintly Grainy. 3 Insoluble. *NLGI-ABEC Spindle Test.

As seen by the preceding table, the compositions of amount of lubricating oil and about 5 to 40 wt. percent the invention represented by Examples I and II have of alkali metal salt of C to C fatty acid, C to C higher dropping points, greater stability against workfatty acid and a polycarboxylic aromatic acid consisting, and a longer lubrication life at 250 F., when coming of a single benzene ring having 2 to 4 carboxy groups, pared to the comparison Composition Awhich is formed in a mole equivalent ratio of about 0.5 to 6.0 mole from the same ingredients but without the phthalic anequivalents of said C to C fatty acid per mole equivalent hydride. It is to be noted that the total amount of of said aromatic acid and about 0.5 to 3.0 mole equivathickener of Composition A lies between that of Exlents of said C to C fatty acid per mole equivalent of amples I and II so that these differences in properties are said aromatic acid. not due to a difference in the amount of total salt t-hick- 2. A lubricating grease according to claim 1 containener present. Also, Examples I and II are seen to be ing 10 to 35 wt. percent of said alkali metal salt wherein superior to Composition B with regard to dropping point said C to C fatty acid is acetic acid and wherein said and lubrication life at 300 F. Composition B repre- 5 alkali metal is lithium. sents a commercially successful lithium grease which has 3. A lubricating grease according to claim 2 wherein found widespread use as a multi-purpose grease, but which said aromatic acid is phthalic acid. is limited in its use at high temperatures. 4. A lubricating grease according to claim 2, wherein In addition, the greases of Examples I and II were said aromatic acid is pyromellitic acid. excellent ball bearing greases as demonstrated bya Ball 5. A lubricating grease consisting essentially of a Bearing Temperature Rise Test. In this test, a 204 mm. major amount of mineral lubricating oil and about 10 steel ball bearing is packed with 3.0 grams of .grease, to 35 wt. percent of lithium salts of acetic acid, C to C and then the bearing is operated at 10,000 r.p.m. while fatty acid, and phthalic anhydride, in a relative mole the temperature of the bearing was measured by thermoequivalent ratio of about 2 to 4 mole equivalents of said couples placed on the outer bearing race. After ten acetic acid per mole equivalent of phthalic anhydride minutes in this test, using the grease of Example I, the and about 1 to 2 mole equivalents of said C to C bearing reached its maximum rise temperature of 10 fatty acid per mole equivalent of said phthalic anhydride. F. above room temperature (75 F.) and then began to 6. A lubricating grease consisting essentially of a major drop. This indicates that the grease was an excellent, amount of mineral lubricating oil and about 10 to 35 quick-channeling grease. That is, the grease had quickly Wt. percent of lithium salt-s of acetic acid, C to C formed a channel for the rotating balls. Such channeling fatty acid and pyromellitic dianhydride in a relative mole properties are important for ball bearing greases since equivalent ratio of about 2 to 4 mole equivalents of said it reduces power consumption which would otherwise be acetic acid per mole equivalent of pyromellitic dianhywasted by the churning of a non-channeling grease. The dride and about 1 to 2 mole equivalents of said C to grease of Example 11 was also a quickchanneling grease, C fatty acid per mole equivalent of said pyromellitic although a little slower than the grease of Example I. dianhydride.

Specifically, the grease of Example II reached a max1- References Cited by the Examiner mum temperature use of 20 F. above the room temperature (75 F.) in twenty minutes and then the tempera- UNITED STATES PATENTS ture fell until it returned to about room temperature. 2,908,645 10/ 1959 Moi-way 252-40 The grease of Example III was also an excellent grease, 3 223,624 12/1965 Murway l; l 252- -41 X although it had a very faint grainy appearance. This 3,233,633 12/1965 Morway et a1 252-41 X grease also had a good high temperature lubrication life at 300 R, which was in excess of 500 hours and still DANIEL Pnma'y Examiner running. I. VAUGHN, Assistant Examiner. 

1. A LUBRICATING GREASE CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF LUBRICATING OIL AND ABOUT 5 TO 40 WT. PERCENT OF ALKALI METAL SALT OF C2 TO C6 FATTY ACID, C10 TO C30 FATTY ACID AND A POLYCARBOXYLIC AROMATIC ACID CONSISTING OF A SINGLE BENZENE RING HAVING 2 TO 4 CARBOXY GROUPS, IN A MOLE EQUIVALENT RATIO OF ABOUT 0.5 TO 6.0 MOLE EQUIVALENTS OF SAID C2 TO C6 FATTY ACID PER MOLE EQUIVALENT OF SAID AROMATIC ACID AND ABOUT 0.5 TO 3.0 MOLE EQUIVALENTS OF SAID C10 TO C30 FATTY ACID PER MOLE EQUIVALENT OF SAID AROMATIC ACID. 